In this study, the pullout resistance of deformed shape memory alloy fibers embedded in a mortar matrix is investigated to develop self crack-closing capacity. Three types of deformed shape memory alloy fibers (dog bone–shaped, end-deformed, and crimped) and one type of smooth shape memory alloy fiber, fabricated from two different alloys, NiTi and NiTiNb, were embedded in a mortar matrix with a compressive strength of 55 MPa. The pullout resistance differed considerably depending on the geometry of the fiber and composition of the alloy. The pullout resistance was generally higher for deformed shape memory alloy fibers than for the smooth shape memory alloy fiber. Among the deformed shape memory alloy fibers, dog bone–shaped fibers showed the highest enhancement in bond strength after heat treatment. The pullout resistance was higher for the NiTiNb alloy than the NiTi alloy when the shape memory alloy fiber was deformed, whereas the relationship was reversed when the shape memory alloy fiber was smooth.

This study investigated the prestressing effect of cold-drawn short NiTi shape memory alloy (SMA) fibres in steel reinforced mortar beams. The SMA fibres were mixed with 1.5% volume content in a mortar matrix with the compressive strength of 50 MPa. The SMA fibres had an average length of 34 mm, and they were manufactured with a dog-bone shape: the diameters of the end- and middle-parts were 1.024 and 1.0 mm, respectively. Twenty mortar beams with the dimensions of 40 mm × 40 mm × 160 mm ( B × H × L ) were prepared. Two types of tests were conducted. One was to investigate the prestressing effect of the SMA fibres, and the beams with the SMA fibres were heated at the bottom. The other was to assess the bending behaviour of the beams prestressed by the SMA fibres. The SMA fibres induced upward deflection and cracking at the top surface by heating at the bottom; thus, they achieved an obvious prestressing effect. The beams that were prestressed by the SMA fibres did not show a significant difference in bending behaviour from that of the SMA fibre reinforced beams that were not subjected to heating. Stress analysis of the beams indicated that the prestressing effect decreased in relation to the cooling temperature.

In this study, mortar beams reinforced by shape memory alloy (SMA) fibers of NiTi and NiTiNb alloys were prepared to perform crack-repairing tests using three-point bending tests. The SMA fibers had a length of 30 mm, and their types were straight, dog-bone, and dog-bone with paper wrapping. For the bending tests, twelve types of mortar beams with the dimensions of 40 mm × 40 mm × 160 mm ( B × H × L ) were prepared. Half of them had a top steel reinforcement, and equal numbers of beams were assigned to the NiTi and NiTiNb fibers. Five SMA fibers were located at the bottom center of the beams along with an artificial crack of 10 mm depth and 1 mm thickness. Epoxy was used to fill the cracks to bond the cracked surfaces using injection, and a hot-gun was used to heat the SMA fibers in the cracks. The crack widths were measured before and after the cracks were repaired, and force–displacement curves were obtained to assess the flexural strength recovery ratio of the beams. It does not appear that the crack-closing capacity of SMA fibers is a crucial factor to recover the flexural strength in repaired beams. However, adequate application of epoxy is critical for repairing cracks, and the residual stress of SMA fibers seems to contribute to increase flexural strength of repaired beams. The residual stress of SMA fibers functions as prestress on mortar and delays the initiation of cracking.

The seismic performance of bridge structures is significantly affected by their column height, design era, and horizontal deck curvature. However, existing risk assessment platforms do not appropriately account for the effect of column height and horizontal deck curvature. This paper investigates the effect of column height, design era, and deck curvature on probabilistic seismic demand models and fragilities of bridges. This paper selects a typical configuration of horizontally curved concrete box-girder bridges in California: two-frame five-span bridges with single-column bents. Extensive nonlinear time history analysis results for the bridges including the uncertainties are initially compared using a statistical technique, analysis of covariance. Results from the analysis of covariance are used to estimate the influence of column height, design era, and horizontal deck curvature on bridge performance. An increase in the deck horizontal curvature is found to increase the bridge vulnerability irrespective of the design era and height range. Although the seismic vulnerability of bridges constructed prior to 1970 increases with the increase in the column height, there is no specific trend in the change in vulnerability with respect to column height for bridges constructed after 1970. This research also shows that the implementation of seismic design principles reduces the seismic vulnerability of the bridges.

This study investigated the recovery stress and bond resistance of cold drawn crimped SMA fiber using two different initial diameters of 1.0 and 0.7 mm. These characteristics are important to the active prestressing effect and crack-closing of the fiber. NiTi SMA fiber was used for the cold drawing, and then crimped shapes were manufactured with various wave heights. After that, tensile, recovery, and pullout tests were conducted. The cold drawn crimped fiber showed softening tensile behavior more clearly than the cold drawn straight fiber when not subjected to heating, whereas they had the same tensile behavior under heating. The recovery stress and the residual stress of the crimped fibers were less than those of the straight fiber with the same diameter. Moreover, crimped fibers with a large diameter and higher wave height would induce more recovery stress and residual stress. The maximum pullout resistance of the crimped fiber was a function of the wave depth, embedded length, yield strength, and flexural rigidity of the fiber.